The present invention relates generally to asynchronous machines, and more particularly to an asynchronous machine with a short-circuit rotor that is rotatably mounted by means of rolling bearings.
The rolling bearings of such machines are generally lubricated with grease. In asynchronous motors, high temperatures are reached in the rotor and thus also at the bearings. Therefore, lubricating greases which ensure sufficient lubrication of the bearings, even at high bearing temperatures, must be used. Such lubricating greases have the disadvantage, however, that they become solid at low temperatures. At temperatures below or near the freezing point, such lubricating greases can become so solid that they completely lose their lubricating effect. If a motor is operated when such conditions are present, damage to the rolling bearings occurs. This can lead to complete failure of the motor, if not immediately, then eventually if the motor is repeatedly started up under the aforesaid conditions. Motors that are used outdoors, for example in electric vehicles, are particularly exposed to large temperature fluctuations.
The present invention is directed to the problem of developing an asynchronous machine of this kind in such a way that damage to the grease-lubricated bearings of the machine is prevented even if the machine is started up in a temperature range below or near the freezing point.